Well it has happened man! We aren't infallible. You're a human just like the rest of us. I think you are in a good place to have forgotten and owned up to it. I think that shows more character than just forgetting and saying oh well and moving on.
I hear you on having them around in our heads more when they are gone than when they are here. I have some things that I'd love to run by my grandfathers if they were still around, or my grandmothers that I didn't get to know. I think that's pretty common and is a good thing in my opinion. We are trying to see life through the lens of someone who we looked up to and respected, to see if we can figure out what they would have done.
At least with forgetting and then remembering later, you aren't coming down with early alzheimers! That's a bonus.
Damn man that was a wholesome song! Who says a love story is only sung best by Blue Eyes or Michael Bublé?